2.0 Analysis 2.1 Take-off Direction The combination of wind direction and take-off direction produced a tail-wind component of 5 to 10 knots during the take-off run. However, the aircraft does not have any published downwind take-off limits, and the wind and water conditions at take-off imposed no unusual stresses on the aircraft. Therefore, the pilot's choice of take-off direction did not contribute materially to the occurrence. 2.2 Aircraft Loading Because the weight of the aircraft was under the maximum gross weight and the centre of gravity of the aircraft was within the prescribed limits, the loading of the aircraft did not impose any unusual stresses on the aircraft, or contribute materially to the occurrence. 2.3 Float Separation Because the eyebolt fitting connecting the diagonal strut to the rear swivel fitting was found bent and broken in overload, with no pre-existing damage, it is likely that the fitting failed during the float separation sequence, but did not initiate the failure. After examination of the front swivel fitting and mounting pad, the Engineering Branch concluded that the attaching bolt probably did not break, but moved out of position, either because the nut was not installed or because it came off during service. Given that the pilot reportedly checked the float fittings before departing the first flight of the day, it is likely that the bolt moved out of the fitting during the two flights completed on the day of the occurrence. Because of the low-wing design of the aircraft, the location of the main entry/exit door, and the seaplane landing gear configuration, a defect in the area of the forward float fittings would be less noticeable than in other aircraft designs. In light of the lack of damage to the front diagonal strut fittings and the overload failure damage found in the other float fittings, it is likely that the departure of the bolt from the front swivel fitting initiated the sequence of failures that resulted in the separation of the float from the aircraft during the occurrence. 2.4 Fasteners Because the bolt and nut connecting the front swivel fitting to the float mounting pad were not recovered, no definitive statement can be made about the type of nut that was installed. However, 9 of the 10 float fitting bolts for which castellated nuts were specified were recovered with fibre locking nuts, and it is possible that this bolt was also secured with a fibre locking nut. Several of the left float fittings that were recovered had less than one thread of bolt extension past their fibre-locking nuts, and it is possible that the missing bolt lost its nut because the nut did not lock securely, and departed from the bolt in service. All of the float attachment bolts and nuts that were recovered were in good condition, with little evidence of wear or corrosion. It is likely that the missing bolt and nut were inspected and replaced at the same intervals as the other attachment bolts, and were probably not worn or corroded to the extent that they contributed to this occurrence. 2.5 Inspection Schedule The Bristol float service manual specifies an inspection schedule which is more rigorous than the one called for in the Transport Canada approved inspection schedule. Although the operator's inspection approval conditions require it to incorporate other applicable mandatory requirements of components installed in its aircraft and amend its inspection schedule accordingly, there is no record of changes to the inspection schedule to reflect the Bristol inspection provisions. Transport Canada did not insist on these provisions and reportedly encouraged some operators to incorporate an inspection schedule which differed from the Bristol inspection requirements. 2.6 Survival Aspects Although the passengers did not wear their life-jackets during the take-off, the pilot's pre-take-off briefing and his actions in retrieving five of the life-jackets as the aircraft was sinking contributed to the survival of the passengers. 3.0 Conclusions 3.1 Findings The pilot was certified and qualified for the flight in accordance with existing regulations. The pilot's choice of take-off direction did not contribute materially to the occurrence. Although the left front swivel fitting attachment bolt was not recovered after the occurrence, it was probably not worn or corroded to an extent that contributed to the occurrence. It is likely that the left front swivel fitting attachment bolt moved out of position, during or before the take-off run, because the securing nut was either not installed or came off in service. The departure of the left front swivel fitting attachment bolt initiated a series of failures that resulted in the separation of the float from the aircraft during the take-off run. The aircraft's low-wing design and landing gear configuration made it less likely that defects in the area of the forward float fittings would be noted during service and operation. The operator's Beech 18 inspection schedule did not incorporate the Bristol inspection requirements for EDO 56-7850 floats. Transport Canada did not insist that the component manufacturer's inspection requirements be included in the operator's Beech 18 inspection schedule. Nine of the 10 float fitting bolts for which castellated nuts were specified were recovered with fibre locking nuts. 3.2 Causes The left front swivel fitting attachment bolt probably moved out of position because the securing nut was either not installed or came off in service. A series of failures ensued, culminating in the separation of the left float from the aircraft. 4.0 Safety Action 4.1 Action Taken The Bristol inspection requirement for EDO floats calls for removal and inspection of the floats every 500 hours, or at the end of each float-flying season. Transport Canada (TC) did not require that the component manufacturer's inspection criteria be incorporated into the approved inspection schedule. A TSB Aviation Safety Advisory was forwarded to TC indicating that TC may wish to review the direction it provides to Approved Maintenance Organizations (AMOs) with regards to following the manufacturer's inspection requirements.